package work;

public class PriorityQueue {
    public int[] elem;
    public int usedSize;

    public PriorityQueue() {
        elem = new int[100];
        usedSize = 0;
    }

    /**
     * 建堆的时间复杂度：
     *
     * @param array
     */
    public void createHeap(int[] array) {
        if(array.length > elem.length){
            elem = new int[array.length];
        }
        System.arraycopy(array, 0, elem, 0, array.length);
        int lastLeaf = usedSize - 1;
        int lastParent = (lastLeaf - 1)/2;
        for(int i = lastParent;i >= 0;i--){
            shiftDown(i,usedSize);
        }
    }

    /**
     *
     * @param root 是每棵子树的根节点的下标
     * @param len  是每棵子树调整结束的结束条件
     * 向下调整的时间复杂度：O(logn)
     */
    private void shiftDown(int root,int len) {
        int parent = root;
        int child = 2 * parent + 1;
        while(child < len){
            if(child + 1 < len&&elem[child] < elem[child + 1]){
                child = child + 1;
            }
            if(elem[child] > elem[parent]){
                int tmp = elem[child];
                elem[child] = elem[parent];
                elem[parent] = tmp;
                parent = child;
                child = 2 * parent + 1;
            }else{
                break;
            }
        }
    }


    /**
     * 入队：仍然要保持是大根堆
     * @param val
     */
    public void push(int val) {
        if(isFull()){
            elem = new int [(int)(usedSize * 1.5)];
        }
        elem[usedSize++] = val;
        shiftUp(usedSize - 1);
    }

    private void shiftUp(int child) {
        while(child > 0){
            int parent = (child - 1)/2;
            if(elem[child] > elem[parent]){
                int tmp = elem[child];
                elem[child] = elem[parent];
                elem[parent] = tmp;
                child = parent;
            }else{
                break;
            }

        }
    }

    public boolean isFull() {
        return usedSize == elem.length;
    }

    /**
     * 出队【删除】：每次删除的都是优先级高的元素
     * 仍然要保持是大根堆
     */
    public void pollHeap() {
        if(isEmpty()){
            throw new RuntimeException("队列为空");
        }
        int tmp = elem[0];
        elem[0] = elem[usedSize - 1];
        elem[usedSize - 1] = tmp;
        usedSize--;
        shiftDown(0,usedSize);
    }

    public boolean isEmpty() {
        return usedSize == 0;
    }

    /**
     * 获取堆顶元素
     * @return
     */
    public int peekHeap() {
        if(isEmpty()){
            throw new RuntimeException("队列为空");
        }
        return elem[0];
    }
}